Carbon dioxide refrigeration system

Abstract

A method and apparatus to refrigerate air in a compartment wherein liquid dioxide is delivered through a first primary heat exchanger such that sufficient heat is absorbed to evaporate the liquid carbon dioxide to form pressurized vapor. The pressurized vapor is heated in an external heat exchanger to prevent solidification of the pressurized carbon dioxide when it is depressurized to provide isentropic expansion of the vapor into a secondary heat exchanger. Pneumatically driven motors are driven by the pressurized carbon dioxide vapor to move air across the heat exchangers. Orifices in inlets to the motors and solenoid valves in flow lines to the motors keep the vapor pressurized while the external heat exchanger supplies sufficient heat to prevent solidification when it expands through the motors.

Having thus described the invention, I claim: 
     
       1. A method of refrigerating air in a compartment comprising the steps of: delivering liquid carbon dioxide through an evaporator means such that sufficient heat is absorbed from the air in the compartment to evaporate the liquid carbon dioxide to form a pressurized vapor;   heating the pressurized carbon dioxide vapor that is exhausted from the evaporator means to prevent solidification of the carbon dioxide when the pressure is reduced to atmospheric pressure; and   depressurizing the carbon dioxide vapor to provide isentropic expansion of the vapor into a heat exchanger means so that additional heat is absorbed from the air in the compartment.   
     
     
       2. A method of controlling the heat transfer rate through a wall of a tube in a compartment comprising the steps of: delivering liquid carbon dioxide into the tube;   moving fluid in the compartment in heat exchange relation with the tube such that heat of the fluid is absorbed by the carbon dioxide to form pressurized carbon dioxide vapor in the tube;   circulating the pressurized carbon dioxide vapor out of the compartment;   heating the pressurized carbon dioxide vapor;   delivering the heated carbon dioxide vapor to drive a pneumatic motor driven fan to move the fluid in the compartment in heat exchange relation with the tube; and   controlling the flow of heated carbon dioxide vapor to the pneumatic motor to prevent solidification of the carbon dioxide as the carbon dioxide depressurizes upon reaching the pneumatic motor chambers.   
     
     
       3. The method of claim 2, with the addition of the steps of: sensing temperature of carbon dioxide exhausted from the tube; and heating surfaces of the tube when the temperature of carbon dioxide flowing to the motor driven fan is less than a predetermined temperature. 
     
     
       4. The method of claim 3 wherein the step of sensing temperature of carbon dioxide is accomplished by positioning a temperature sensor in heat exchange relation with carbon dioxide flowing to the motor. 
     
     
       5. The method of claim 3 wherein the step of heating surfaces of the tube comprises: heating a volume of carbon dioxide; and delivering the heated carbon dioxide through the tube. 
     
     
       6. The method of claim 5 with the addition of the steps of: sensing the temperature of the surface of the tube; and terminating heating of the surfaces of the tube when the tube surface increases to a predetermined temperature. 
     
     
       7. A method of controlling temperature in a compartment comprising the steps of: circulating liquid carbon dioxide through a primary coil such that the carbon dioxide absorbs heat;   changing the enthalpy of the carbon dioxide by heating the carbon dioxide exhausted from the primary coil to assure that the carbon dioxide is in a vapor phase;   delivering the heated carbon dioxide vapor through a pneumatic motor arranged to drive a fan; and   circulating the carbon dioxide exhausted from the motor through a secondary coil, the primary and secondary coils being positioned such that the motor moves air within the compartment in heat exchange relation with the coils.   
     
     
       8. The method of claim 7 with the addition of the steps of: stopping the flow of the liquid carbon dioxide to the primary coil when a predetermined quantity of ice has formed on surfaces of the primary coil; and   directing heated carbon dioxide vapor through the primary coils, through the motor, and through the secondary coil for melting ice on the surfaces of the primary coil.   
     
     
       9. Temperature control apparatus comprising: a coil;   means to deliver pressurized fluid carbon dioxide through said coil so that the carbon dioxide absorbs heat from the atmosphere surrounding said coil to form pressurized carbon dioxide vapor;   means for heating the pressurized carbon dioxide vapor that is exhausted from said coil to prevent solidification of the carbon dioxide when the pressure is reduced to atmospheric pressure;   depressurizing the heated carbon dioxide vapor to provide isentropic expansion of the vapor into heat exchanger means so that additional heat is absorbed from the atmosphere surrounding said coil;   means to move the surrounding atmosphere across said coil;   first sensor means to sense temperature of carbon dioxide exhausted from said coil;   second sensor means to sense the temperature of the surface of said coil;   means to generate a signal when the temperature of the carbon dioxide exhausted form said coil is less than a predetermined temperature;   means energized by the signal to heat surfaces of said coil to melt ice thereon; and   means energized by said second sensor to terminate heating of the surfaces of said coil.   
     
     
       10. The combination called for in claim 9 wherein the means to move air across said coil comprisers: a fluid driven motor connected in driving relation with impeller means; and means to direct fluid from said coil through the motor. 
     
     
       11. Temperature control apparatus according to claim 10 with the addition of orifice means adjacent the inlet to said fluid driven motor. 
     
     
       12. Temperature control apparatus according to claim 11 with the addition of flow control valve means in said means to direct fluid through said motor. 
     
     
       13. The combination called for in claim 9 wherein the means energized by the signal to heat the surfaces of said coil comprises: heater means;   signal responsive valve means arranged to deliver carbon dioxide to the heater means; and   means to deliver heated carbon dioxide from the heater means to said coil.   
     
     
       14. The combination called for in claim 9 wherein the means to deliver fluid through the coil comprises: a container; conduit means connected between said container and the coil; and means in said conduit means for controlling the flow of carbon dioxide therethrough. 
     
     
       15. Apparatus to control temperature in a cargo compartment of a trailer comprising: a source of liquefied carbon dioxide carried by the trailer;   an evaporator means in the compartment;   said evaporator means for causing the liquefied carbon dioxide to absorb sufficient heat from within the compartment so that the liquefied carbon dioxide is evaporated to form pressurized carbon dioxide vapor,   first conduit means connecting said evaporator means and said source of liquefied carbon dioxide;   heat exchanger means;   second conduit means connecting said heat exchanger means with said evaporator means; and   a pneumatically operated motor;   a fan mounted to be driven by said motor, said fan arranged to cause air in the compartment to circulate over the surfaces of said evaporator means;   third conduit means connecting said heat exchanger means with said motor; said motor being driven by the release of the pressurized carbon dioxide vapor to atmospheric pressure, and   said heat exchanger means for heating the carbon dioxide sufficiently to prevent solidification of the carbon dioxide when the carbon dioxide becomes depressurized in said motor.   
     
     
       16. The combination called for in claim 15 with the addition of: temperature sensor means adapted to sense the temperature of vapor delivered to said motor; and controller means adapted to defrost said evaporator when the temperature of vapor drops to near the freezing point of carbon dioxide.